The present invention relates generally to an ion beam processing apparatus and a method of operating an ion source therefore, and more particularly to a method of operating an ion source to extract, as an ion beam, ions within a plasma generated in the ion source for use in an ion beam processing apparatus for performing ion beam milling, ion beam sputtering and so on, and a method of operating an ion beam processing apparatus which uses the ion source.
The ion beam processing apparatus employs positive ions which, when irradiated to collide with a workpiece, cause accumulation of a positive charge on the surface of the workpiece, so that the ion beam processing apparatus cannot continuously collide a sufficient ion beam against a processed site on the workpiece. For this reason, a neutralizer has been conventionally provided for irradiating the surface of a workpiece with electrons to maintain the surface of the workpiece in an electrically neutral state.
The neutralizer is operated to fill a processing chamber which contains a workpiece with electrons prior to the processing on the workpiece such that the neutralization on the surface of the workpiece can be started simultaneously with the irradiation of an ion beam to the workpiece.
Conventionally, an ion generator typically produces a plasma to generate ions when the ion source is started, while the neutralizer produces electrons within the processing chamber. It is therefore required to provide a shielding feature for preventing the electrons from flowing into the ion generator from the processing chamber. Such a shielding feature is implemented by initially activating a deceleration power supply in an ion source to apply a deceleration electrode with a negative voltage, and subsequently activating an acceleration power supply to apply an acceleration electrode with a positive voltage.
However, when an ion source operating method as mentioned above is applied to the ion beam processing apparatus, particles possibly attached on the electrodes of the ion source to form short-circuiting between the acceleration electrode and the deceleration electrode would cause repeated breakdowns of the deceleration power supply which has been first activated.
The breakdown of the ion source power supply mainly results from the short-circuiting between the electrodes of the ion source due to particles attached thereon. Such particles are in most cases electrically conductive materials which are sputter deposits once attached on and coming off of a wall surface within the processing chamber. When the acceleration electrode and the deceleration electrode of the ion source are applied with respective voltages with such particles attached on portions of these electrodes, the two electrodes are short-circuited to cause a sequence of repeated operations involving a short-circuit current flowing into the ion source power supply, the ion source power supply being shut down in response to a detected excessive current, and the voltage applied again after a predetermined time period. This sequence of operations will be repeated until the particles causing the short-circuiting are burnt away or removed from the electrodes by the short-circuiting current.
Typically, in the ion source power supplies, the acceleration power supply is designed to have a larger current capacity than the deceleration power supply. For example, an ion source power supplies may be a combination of an acceleration power supply having a maximum output of 1.3 kv, 3 A and a deceleration power supply having a maximum output of 500 v, 0.2 A. This is because the acceleration and deceleration power supplies need not have the same capacity in view of the optimization for the configuration of the entire ion source power supplies. More specifically, the acceleration power supply is required to supply an ion beam current when an ion beam is extracted, whereas the deceleration power supply hardly has to supply a current for the ion beam.
In addition, values for detecting excessive currents of the respective power supplies are typically set in proportion to the rated maximum current values of the respective power supplies, so that the excessive current detection functions at a lower excessive current for a power supply having a smaller current capacity. Thus, if particles are attached on portions of the electrodes of the ion source, a short-circuiting current flows through particles when a deceleration voltage is applied, and activates the excessive current detection in the deceleration power supply to once shut down the deceleration power supply. Then, in a predetermined time period, the deceleration voltage is again applied. This sequence of operations is repeated to keep the acceleration power supply from activating indefinitely.
Further, with particles of small size, a short-circuiting current flowing through such particles results in burning off and consequently removing the particles from the electrodes. However, if particles have a certain large size, a short-circuiting current flowing in the deceleration power supply having a small capacity is not enough to burn off the particles which are therefore left on the electrodes, thus forcing the ion source to repeat a sequence of operations involving excessive current detection, trip (breakdown) and re-activation.
For the user of these apparatus, it is important to operate the apparatus in a stable state for a long period, minimize maintenance operations such as cleaning for the apparatus, and increase an apparatus available time resulting from the minimized maintenance operations. For achieving these objects, it is critical to minimize the frequency of the occurrence of breakdown, activate the apparatus in a stable state as early as possible, and maintain the stable operating state.
Generally, the breakdown frequently occurs in the ion source due to particles attached on the electrodes of the ion source upon powering on the apparatus after cleaning the inside of the apparatus or after cleaning the electrodes of the ion source. A conventional method of operating the ion source, however, suffers from difficulties in removing particles, contributing to the breakdown, from the electrodes of the ion source, and consequent occurrence of repeated breakdowns. To reach a stable operating state substantially free from the breakdown, a long time is required. In some cases, the electrodes of the ion source must be frequently cleaned in order to improve such situations, thus experiencing difficulties in improving the apparatus available time.
In view of the problems inherent to the prior art as mentioned above, it is an object of the present invention to provide an ion beam processing apparatus and a method of operating an ion source therefor which are capable of reducing the frequency of the occurrence of breakdown to smoothly activate the ion source, as well as accomplishing reduced requirements for maintenance such as cleaning the electrodes of the ion source and so on, a higher reliability and an improved operating efficiency of the apparatus.
According to the present invention, an ion source is mounted to a processing chamber to form a vacuum chamber into which a gas is introduced to produce a plasma, and an electric field is applied within the vacuum chamber to extract ions within the plasma as an ion beam. The ion source comprises an arc power supply, an acceleration power supply for applying an acceleration electrode with a positive potential to extract an ion beam, and a deceleration power supply for applying a deceleration electrode with a negative potential to prevent ions from flowing into the ion source. When the ion source is operated, the acceleration electrode is first applied with a positive potential, and the deceleration electrode is applied with a negative potential after or simultaneously with the application of the acceleration electrode with the positive potential.